flatArray

flatArray.js

const foo = [{
  key: 'first'
}, {
  key: 'second'
}, {
  key: 'third'
}, {
  key: 'more',
  children: [{
    key: 'fourth'
  }, {
    key: 'fifth'
  }, {
    key: 'more',
    children: [{
      key: 'sixth'
    }, {
      key: 'seventh'
    }]
  }]
}]

function flatArray(array, prop, decideFunc) {
  if (Object.prototype.toString.call(array) !== '[object Array]') {
    throw new TypeError('The type of first argument must be an array');
  }
  if (typeof prop !== 'string') {
    throw new TypeError('The type of second argument must be a string');
  }
  if (decideFunc && Object.prototype.toString.call(decideFunc) !== '[object Function]') {
    throw new TypeError('The type of third argument must be a function');
  }
  let result = [];
  array.map(item => {
    if (!(prop in item)) {
      result.push(item);
    } else {
      if (decideFunc && decideFunc(item)) {
        const child = item[prop];
        const tmp = flatArray(child, prop, decideFunc);

        result = [...result, ...tmp];
      } else {
        result.push(item);
      }
    }
  });

  return result;
}
flatArray(foo, 'children')

/*
[{
  key: 'first'
}, {
  key: 'second'
}, {
  key: 'third'
}, {
  key: 'fourth'
}, {
  key: 'fifth'
}, {
  key: 'seventh'
}]
*/